A display case is an item which you do not use directly. Rather, it simply sits there as an empty glass or plastic box until you put something under it or inside of it. Until that happens it is entirely worthless, but up until that point it is a very important.
If you have a dream about a display case then it depends what is on the display case for you to find real depth in the interpretation. Still though, as long as you remember, you can infer your own conclusions from what you saw in the case. Basically if you have a dream of a display case, then whatever it is that is in the display case is something that you would be very protective of in real life. Perhaps they are photos of cherished family memories or family members. Or maybe they are photos of your actual family members and you feel incredibly close to them. That could always be one meaning.
Perhaps if you have a dream about an empty display case this means that you need to pick one of your talents to put on display. You are a very shy person and your dream is trying to let you know that it is time for you to really put yourself out there and show others that you have some worth and that you really do matter. You need to display to people some of your best qualities so that they have something to judge you by.